(1) Field of the Invention
Because more and more corn grain is diverted to ethanol production from use as a food, food shortage concerns have arisen. However, ethanol made from cellulosic materials such as stems, leaves, stalks and trunks of plants instead of corn grain would ameliorate concerns over the food supply. Furthermore, any cellulosic biomass for ethanol production can be converted to butanol as well for auto fuel. Butanol is in several ways more similar to gasoline than is ethanol. Butanol can, therefore, be used by itself as fuel in internal combustion engines and has been demonstrated to work in some vehicles designed for use with gasoline without any modification. Butanol can be produced from biomass as well as fossil fuels. Butanol produced via fermentation is called biobutanol to reflect its origin, although it has the same chemical properties as butanol produced from petroleum. Butanol is currently an industrial commodity and mainly manufactured from petroleum, with a 370 million gallons per year market with a selling price of about $3.75 per gallon. Indeed, butanol has higher energy content (110,000 Btu per gallon for butanol as compared to 84,000 Btu per gallon for ethanol). Gasoline contains about 115,000 Btu's per gallon. Butanol is six times less “evaporative” than ethanol and 13.5 times less evaporative than gasoline, making it safer to use as an oxygenate in Arizona, California and other “hot” states, thereby eliminating the need for very special blends during the summer and winter months. There has been little to no effort to promote butanol as an alternate fuel because of historically low yields and low concentrations of butanol being produced through Acetone-Butanol-Ethanol (ABE) fermentation compared to those of ethanol.
(2) Description of Related Art, Including Information Disclosed Under 37 C.F.R. Sections 1.97 and 1.98.
Acetone/butanol/ethanol (ABE) is an anaerobic fermentation process capable of producing commodity chemicals, such as butanol and acetone, from biomass. It is known in the art that Clostridium acetobutylicum can be used as the bacterium in ABE fermentation. For example, U.S. Pat. No. 5,192,673, the entire contents of which are incorporated herein by reference, describes an improved fermentation process for producing high levels of butanol using a mutant strain of Clostridium acetobutylicum designated Clostridium acetobutylicum ATCC 55025.
After cellulose, lignin is the most abundant biomass found in nature. Lignin fills the spaces in the plant cell wall between cellulose, hemicellulose and pectin components. The paper industry produces a great deal of lignin in the form of a substance known as “black liquor,” from the pulping process which essentially delignifies wood chips to form paper-making fibers. Black liquor is an aqueous solution of lignin residues, hemicellulose, and inorganic chemicals used in the pulping process wherein wood is delignified into wood fibers, lignin and hemicellulose.
Wheat straw, which is a waste product in most agricultural operations, is a type of cellulose that is relatively easy to delignify. Over 126 million metric tons of wheat straw are produced in the United States every year. For this reason, wheat straw has been targeted as feedstock to convert to a biobutanol fuel.